High frequency transmitter



May 15, 1934.

MODULATOR Filed Dec. 1931 E. GREEN HIGH FREQUENCY TRANSMITTER INVENTOR ERNEST GREEN BY /z/m/M/ ATTORNEY Patented May 15, 1934 UNITED STATES PATEN OFFICE I HIGH FREQUENCY TRANSMITTER of Delaware Application December 1, 1981; Serial No. 578,383 In Great Britain December 2, 1930 2 Claims.

This invention relates to high frequency transmitters and more particularly to radio and similar carrier wave telephone transmitters.

The invention has for its object to provide an improved transmitter arrangement whereby the transmitter proper may be rendered active or inactive under the control of the voice or other signals to be transmitted. As is well known such control is desirable in high power radio telephone transmitters and like installations inter alia in order to prevent echo and singing round a circuit, and to prevent carrier noise in the receiver on ship installations, and the like.

According to the present invention a radio or like transmitter is rendered active and inactive under the control of the voice or other signals to be transmitted by means of a rectifier to which the voice or other signal voltages are applied said rectifier containing in its output circuit a leaky condenser unit the voltage across which is utilized to render the transmitter active and inactive by controlling what may be termed a keying arrangement, i. e. an arrangement whereby the transmitter may be in effect turned on or off. 5 Preferably the desired keying effect is obtained by controlling an absorber valve arrangement which diverts the anode feed from a valve or valves in the transmitter proper under the control of the voltage across the leaky condenser unit.

The invention is illustrated in the accompanying diagrammatic drawing which shows one way of carrying out the invention as applied to a radio telephone transmitter.

Referring to the drawing speech input, e. g. from a land-line is applied between grids 1 and 2 and cathodes 3 and a respectively of a pair of thermionic valves V1 V2 whose grids and cathodes are connected together each to each. The anode 5 of the valve V1 is connected through a choke L1 4.0 to a source of anode potential 8 (120 volts say) and through a condenser C1 and the primary of y a transformer T1 in series to earth. The secondary of the transformer leads as in the usual way to a modulator 9. The anode 10 of the valve V2 is variably tapped onto one of a pair of resistances R1 R2 in series, the two separate resistances together constituting a shunt across the primary 12 of an inter-valve transformer T2 whose secondary 14 is connected between grid and cathode of an audio frequency amplifying valve V2. The two resistances R1 R2 are as shown in series in a loop circuit with the primary of the transformer T2 and may conveniently be of 5000 ohms and 8000 ohms respectively. The secondary of the transformer T2 may be shunted by the usual stabilizing resistance R3.

The audio frequency amplifier valve V2 is choke-capacity coupled by means of a system L2 C3 L3 to a second audio frequency amplifier valve 61} V4! whose output circuit is transformer coupled by a transformer T3 to the input circuit of a diode rectifier V5 which may be conveniently constituted by a triode having its grid and anode connected together as shown. The choke L2 is shunted 65 by a condenser C2 of such magnitude as to render 1' the combination sensitive to voice frequencies but insensitive to the considerably higher frequencies likely to constitute undesired noise or background. One end of the secondary winding of 7Q the coupling transformer T3 is connected to the grid-anode connection of the rectifier V5 and the other end to the positive terminal of a battery B1 whose negative terminal is connected through a condenser C4 of say one microfarad shunted by a leak resistance R4 of say half a megohm to the common cathode connection G. In some cases the battery B1 may be omitted and the transformer terminal connected direct to the condenser 04. Preferably the leak resistance R; is 0 variable. The end of the condenser C4 adjacent the battery B1 is connected to the grids 11 and 12 of a pair of valves V6 V7 connected in parallel. These valves constitute what may be termed a sub-absorber stage. The anodes 17 and 19 of 35 the sub-absorber valves are connected together and through a resistance R5 of say 5000 ohms to the source of anode potential connected at 8. The junction point of the anodes of the sub-absorber control valves V6 V7 with the common anode resistance R5 is connected through a bias battery B2 to the grids 20 and 22 of a pair of sub-absorber valves V3 V9 which are also connected in parallel, the plates 21 and 23 of the valves V8 V9 being connected together and through a resistance R6 of say 150,000 ohms, to a source of main anode potential not shown which may be, for example, 5000 volts and may be connected at HT2. As will be seen all the valves prior to those which are energized from the 5000 volts anode supply are energized from the common anode potential source connected at 8 this being a convenient and preferable arrangement.

The common anode point of the valves V8 V9 is connected through two resistances R7 R8 in series one being of say 20,000 ohms and the other of say 17,000 ohms value and through a battery B3 of say 250 volts to the common cathode connection the said battery having of course its negative terminal connected to the said cathode connection. The junction point of the resistances R1 R8 is connected to the grid 24 of a further triode V10 whose plate 26 is connected through an anode resistance R9 to the 5000 volt supply at I-IT2 and also via a lead to the drive of for example the final power stage of the transmitter 30 to be controlled. The valve V10 may be termed an absorber valve. In the figure various meters which may be provided as desired are indicated by references M in circles. These are however ignored in the preceding description.

The operation of the device will now be given. It will be assumed that modulating frequencies are applied from the line L by way of thermionic amplifier V1 to transformer T1 and by way of thermionic amplifier V2 to the control circuit including the tubes V3, V4, etc. The modulating potentials from T1 will be applied by way of modulator 9 to the transmitter 30 to modulate therein carrier frequency oscillations provided the transmitter is active. The purpose of the present invention is to insure that this transmit ter will be rendered active when voice frequencies are impressed on the line L. This is insured by the control circuit including the tubes V3, V4, etc. The tubes V3, V4 amplify the audio frequency potentials applied from L to V2 and from V2 to V3 by way of the resistors R1, R2 and transformer T2. The purpose of these resistors is to predetermine the amplitude of the signals reaching the tube V4. The tube V3 is coupled by a voice frequency selective circuit L2, C3, L3 to the tube V4. The amplified and filtered audio frequency signals are impressed by way of transformer T3 on to the rectifier V5. V5 converts these potentials into unidirectional current which flows in the resistance R4 and the potentials causing these currents to fiow charges the capacity C4. This flow of current through R4 impresses a high negative potential on the grids of tubes V0, V1 to bias these tubes to cut-off. The tubes are, due to this action, nonconductive. The potential at the upper terminal of R5 rises and with the battery potential B2 increases the potential on the control grids 20 and 22 of tubes V8 and V0 to such a value that these tubes become highly conductive. The tubes being conductive draw current from the source B3 and from the high potential source HT2. Flow of current through the resistance R8 causes a drop in the potential applied to the control grid 24 of tube V10 tobias said tube to cut-off or toward cut-off. The tube V10 now is nonconductive and draws no current from the source HT2. The potential on theanode 26 accordingly rises and is impressed by way of the line to the transmitter 30.

In these circumstances drive is applied to the final power stage of the: transmitter so that said transmitter becomes active. As soon as speech or other signals cease the leaky condenser unit discharges and the transmitter becomes inactive again.

The transmitter 30 may be rendered active in numerous ways. For example, the potential on anode 26 of tube V10 may be used to bias a tube or tubes in the transmitter to a point at which they become operative. Other schemes may be used but since the manner in which this positive potential renders the transmitter active per se forms no part of the present invention, it is thought that it need not be described here other than as described above. It is noted that, in addition to controlling the operativeness of the transmitter 30, the tube V10 also acts to maintain p a constant drain on the source HT2. This is due to the fact that, when the transmitter is rendered operative and is drawing current from the source HT2, the tube V10 is inoperative, that is, biased to cut-off, and draws no current from the source HT2, and when the transmitter is rendered inoperative, so that it takes no current from the source HT2, the tube V10 is conductive and draws current from the source I-IT2.

Where so-called echo suppressors are employed, if it be required to open a line (i. e. to render it operative) when speech or other sig nals are occurring the valves V8 V0 are made part of the speech amplifying system at a point nearer the output than that at which the echo suppressor unit is tapped off. If it be required to close the line (i. e. to render it inoperative) on the occurrence of speech or other signals, the negative voltage developed across the leaky condenser unit may be caused to render a valve or valves, such as the valves V6 V7 in the amplifier inoperative.

In the arrangement particularly described, the apparatus comprising the valves V3 V4 V5 V0 and V7 may be regarded as an absorber control unit, the valves V1 and V2 may be regarded as stages in a land line or equivalent amplifier and the valves V2 V0 and V10 as sub-absorber and absorber valves controlling the transmitter.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:-

1. The combination with a transmitter and a source of signalling potentials to modulate said transmitter of means actuated by signalling potentials from said source for determining the operativeness of said transmitter comprising, a thermionic amplifier having its input electrodes connected to said source of signalling potentials, a thermionic rectifier coupled by way of amplitude regulating means to said thermionic amplifier, a condenser and a resistance in parallel in said rectifier circuit whereby said condenser is charged when signalling potentials from said line are impressed on said amplifier, a thermionic control tube having its input electrodes connected with said condenser and said resistance, an absorber tube having its input electrodes connected with the output electrodes of said control tubes and its output electrodes connected by way of a resistance to the source of potential for said transmitter, and a connection between said last named resistance and the output electrodes of said, absorber tube and said transmitter for rendering said transmitter operative when said absorber tube is nonconductive and vice versa.

2. Signalling means comprising, a transmitter, a thermionic modulator connected therewith, a source of modulating potentials, means for connecting said source of modulating potentials to said modulator, and means for rendering said transmitter operative when voice frequencies are impressed from said source on said modulator comprising, a thermionic amplifier having its input electrodes connected with said source, a second thermionic amplifier having its input electrodes connected through amplitude regulating means with the output electrodes of said first named thermionic amplifier, a third thermionic amplifier having its input electrodes connected through a filter circuit with the output electrodes of said second named thermionic amplifier, a thermionic rectifier having its input electrodes coupled to the output electrodes of said third named thermionic amplifier, a condenser and resistance in parallel in the output circuit of said rectifier, a pair of thermionic control tubes having their control electrodes coupled to said resistance and condenser whereby a negative potential is applied to said control-electrodes when modulating potentials are impressed on said first named amplifier, a charging resistance connected between the anode and cathode of said control tubes, a pair of thermionic absorber tubes having their control electrodes connected through a source of potential to the anodes of said control 

